Event
Proposal Exam: Yidi Shen
Wednesday, October 4, 2023
10:30 a.m.
AVW 2328
Maria Hoo
301 405 3681
mch@umd.edu
ANNOUNCEMENT: Ph.D. Research Proposal Exam
Name: Yidi Shen
Committee:
Professor Alireza Khaligh (Chair)
Professor Sahil Shah
Professor Xin Zan
Date/time: Wednesday, Oct 4th, 2023 at 10:30 AM
Location: AVW 2328
Title: Active Power Decoupling (APD) Converter for PV Microinverter Applications
Abstract: Under global challenges in climate change, the demand for renewable energy is growing continuously. Photovoltaic (PV) power and its integration to the utility grid is gaining more and more traction. To lower the levelized costs of electricity (LCOE) of PV systems, enhancing the adoption of PV applications, and ensuring the delivery of high-quality power to the utility grid, there is a growing need for reliable, cost-effective, efficient and compact PV inverters. One key challenge in single phase PV system reliability is to eliminate the short lifetime electrolytic capacitors used for decoupling the double line frequency (DLF) power. To achieve this goal, active power decoupling (APD) technique is widely required. This Ph.D. research proposes an APD converter circuit which is suitable for PV microinverters, designed for optimized efficiency, power density and cost, and controlled to achieve good power decoupling performance, maximizing the system maximum power point tracking (MPPT) efficiency.
The proposed APD converter circuit is analyzed in terms of low frequency operation principle for power flow and high frequency operation principle for modulation strategy, where different topologies are analyzed considering the voltage and current rating of active devices and decoupling capacitors. Two modulation approaches, continuous conduction mode (CCM) and critical conduction mode (CRM) modulations are compared with detailed zero voltage switching (ZVS) operation analyzed, where CCM enables smaller high frequency current ripple thus lower rms current and inductor core loss, CRM enables full ZVS thus lower switching loss. Parametric design and multi-objective optimization are performed for CCM and CRM to select circuit components and switching frequency for each modulation strategy for minimized power loss, volume and costs. With the results of multi-objective optimization, Pareto-optimal designs for CCM and CRM are analyzed in terms of the impact of switching device output capacitance and on-state resistance, inductor winding turns and core geometries, capacitor dimensions and capacitance to the trade-off between different power loss mechanisms, circuit volume and component prices. Finally, closed-loop control algorithms for optimal CCM and CRM operated APD realizations are designed and the system characteristics are compared, with a simple pulse width modulation (PWM) based control strategy is proposed to implement closed-loop CRM modulation that does not rely on zero-crossing detection. To validate the circuit design, associated analyses and control approaches, hardware prototypes are designed and tested experimentally.
